1. Field of the Invention
The present invention relates generally to antennas and devices for receiving and transmitting microwave signals. In particular, the present invention relates to multiple beam or phased array antennas, antenna feeds, and beamforming networks.
2. Description of the Related Art
In the recent past, the number of satellites placed in geosynchronous orbit about the earth has increased significantly. Associated with the increase in the number of satellites is an increase in the microwave signals being transmitted from the surface of the earth and the noise being generated. Also, some satellite communication systems are susceptible to intentional jamming by those interested in disrupting communication. Therefore, modern antennas and beamforming networks must be more sophisticated to amplify signals of interest while nullifying noise and signals from other areas. In particular, receivers with the capability to produce nulls in pattern coverage to null out high power jamming signals is needed. Additionally, it is advantageous to send signals to a variety of users without wasting power by radiating the signals toward regions where there are no users of interest. There is also a need for the ability to point an antenna beam at a moving target without having to physically move the antenna elements. Therefore, there is a need for multiple beam antennas and beamforming networks with the ability to shape antenna beams for a variety of needs.
In an attempt to satisfy the need for antennas and beamforming networks for satellites, multiple-beam and phased array antennas have been developed. The prior art typically forms antennas and beamforming networks from machined or electro-formed horns, separate filters and delay line or ferrite phase shifters. These devices are coupled to wave guides and coaxial transmission lines as well as other microwave components. However, the configurations of the prior art are relatively large and heavy which is a particular disadvantage since the antennas are used in spacecraft where size and weight are critical because of the tremendous launch costs for spacecraft. These prior art antennas and phased arrays are also very difficult and expensive to implement on a recurring basis because the horns, filters and phase shifters are individual devices with characteristics that vary from device to device. Additionally, it is difficult and expensive to assemble these devices into antennas that will have uniform characteristics throughout the array.
The prior art also includes a variety of other antennas and receiving systems for microwave signals. For example, U.S. Pat. No. 3,953,857 to Jenks discloses an planar phase array that is mechanically rotatable about an axis for providing wider scanning limits for the array; U.S. Pat. No. 4,521,781 to Campi et al. discloses a microstrip antenna array including spaced radiator elements for easy scanning; U.S. Pat. No. 4,652,880 to Moeller et al. discloses an antenna feed network including power dividers to distribute two microwave signals; U.S. Pat. No. 4,734,700 to Brunner discloses an omni-directional scanning group antenna with electronically phase-control beam for precise target location; U.S. Pat. No. 4,766,438 to Tang discloses a lens antenna having four phased array apertures positioned for hemispherical coverage; and U.S. Pat. No. 4,799,065 a reconfigurable beam antenna system including a focusing means, an plurality of antenna elements and a feed network. These devices disclose a variety of antennas, however, none disclose the ability to produce nulls in pattern coverage to decrease the impact of high power jamming signals.
Thus, there is a need for an antenna and beamforming network with reduced size, cost and weight as well as the ability to produce nulls in pattern coverage.